Lunar Meteor Impact Monitoring and the 2013 LADEE Mission

Transcription

1 Lunar Meteor Impact Monitoring and the 2013 LADEE Mission Brian Cudnik Department of Chemistry & Physics Prairie View A&M University P.O. Box 519, M.S Prairie View, Texas Lunar Meteor Impact Monitoring - Cudnik Abstract For over twelve years, amateur and professional astronomers have been monitoring the moon regularly for the tell-tale point-like flashes of impacting meteoroids. This endeavor started with my own visual sighting of a lunar Leonid meteor impacting the dark hemisphere of the waxing gibbous Moon on 1999 November 18 (UT). Since then, the Association of Lunar and Planetary Observers (ALPO) has established the Lunar Meteoritic Impact Search (LMIS) section, which I have served as coordinator since early 2000, and we have logged over 80 lunar meteor impact candidates. In this presentation I will provide a brief overview of lunar meteor monitoring techniques, including some of the equipment that people have been using in the field. I will outline how anyone can become involved in this ongoing, fruitful study of this dynamic aspect of our solar system. Finally I will introduce the upcoming LADEE moon mission and discuss how amateur astronomers can be involved in gathering useful scientific data during the Perseid 2013 maximum, and afterwards, in support of this mission. 1. Introduction Since the invention of the telescope, and even before that, the occurrence of Lunar Transient Phenomena (LTP) has perplexed astronomers, challenging (especially in more recent centuries) the paradigm that the moon is changeless and dead. LTP has taken on many forms, including point flashes that appear and disappear in a fraction of a second, but have only been documented by single observers of varying skill levels. There are relatively rare instances of small groups of people at the same telescope or the same observing site documenting LTP, but no reports of two well-separated observers (by at least 50 km), to my knowledge, have been recorded until Since 1999, when the first scientifically confirmed observations of lunar meteor phenomena were recorded, astronomers at various levels have recorded, fairly regularly, the occurrence of point flashes on the moon caused by meteoroid impacts. These turned out to be much more common than lunar eclipses, but their random nature confounded observations of them for centuries. A handful of systematic attempts at observing and cataloging lunar meteoroid impacts have been attempted throughout the 20 th century, with one of the most notable being the Association of Lunar and Planetary Observers Lunar Meteor Search program which lasted from 1955 to 1965 but failed to provide simultaneous independent observations of lunar meteors. This is not surprising given that the observations were visual at the time, and it is extremely challenging to document a lunar meteor strike solely by pure visual means. But technology (and a little serendipity) would change that near the dawn of the 21 st century. NASA is planning to launch the latest in a series of spacecraft to the moon, in The spacecraft, dubbed Lunar Atmosphere and Dust Environment Explorer (LADEE) is scheduled to launch in 2013 July. Collaborations with universities and the amateur astronomy community are sought for this worthwhile project. 2. Historical Background 2.1 The First Confirmed Lunar Meteor Impact Observations and the Formation of ALPO-LMIS Prior to the uneventful impact of Lunar Prospector in 1999 July, during the fall of 1998, Martin Beech and Simona Nikolova, of the University of Regina, made specific predictions about lunar Leonids, published in their paper (Beech et al., 1998). They realized that the moon would be entering an especially dense filament of meteoroids during the November Leonid meteor shower. David Dunham, president of IOTA (International Occultation Timing Association) coordinated an effort to videotape the unilluminated side of the waxing gibbous Moon during the peak of activity November 18 (3h to 6h UT). At that time, most setups involving video cameras and telescopes were unable to take in the entire 29

2 Moon, so the job was partitioned into thirds. People whose last names began with A through H would monitor the northern third of the moon, etc. so as to cover the entire darkened crescent of the waxing Gibbous moon. Not being equipped with video but having access to a 14-inch f/11 Cassegrain, I visually monitored the moon for impacts and spotted one at 4:46 UT. This was subsequently confirmed on Dunham s video and this confirmation motivated others to check their videos for additional impacts. Initially, six impact events, showing themselves as point flashes of light, were observed and confirmed. New software, developed by Peter Gural, of SAIC (Science Applications International Corporation) for fireball detection was used to located additional impact events on people s videotapes. This method resulted in five additional, unconfirmed impact candidates being found. Astronomical Association, more groups, individuals, and organizations become involved toward the middle of the first decade of the 21 st century. A group from Japan, observing the moon during the Perseid meteor shower of 2004, netted a confirmed Perseid meteoroid impact, the first confirmed non-leonid lunar meteor. A year later, the Meteoroid Environment Office of NASA Marshall Space Flight Center, Alabama, USA, began a regular program to monitor the moon for two weeks per month with multiple telescopes and video cameras. The first impact event candidate was recorded in early 2005 November, a likely Taurid meteoroid. Since then, this program has recorded over 200 meteor impact events on the Moon. The observers who contributed to ALPO-LMIS have, over the years, recorded some 80 viable candidates, but only a handful of these were scientifically confirmed. In most cases, the observer was working alone or happened to be looking at the moon for other reasons when he/she is surprised by an impact event. In recent years, however, with the collaboration with NASA-MSFC, several of our active members have recorded impacts that have been confirmed by NASA and vice versa. Figure 2 shows an image of a lunar Geminid impact that I recorded by video in 2010 December. Figure 1. Image of Leonid impact A recorded on 18 November 1999 by David Dunham (image courtesy of David Dunham). In early 2000, the Association of Lunar and Planetary Observers formed the Lunar Meteoritic Impact Search section, for which I was made the coordinator (and remain so to this day). The section enjoyed much activity in the first year of operation, with many observers reported what would later be deemed as spurious (non-impact) events caused by retinal flashes or cosmic ray hits. By the second year, the activity had tapered off, but enjoyed a brief resurgence in 2001 November when the Moon was once again favorably placed to receive impacts from a relatively dense ribbon of meteoroids from the Leonid stream. Two confirmed and two probable impact candidates were recorded with this event. 2.2 More Organizations get Involved In addition to ALPO-LMIS, IOTA, the Italian Geologic Lunar Researches Group, and the British Figure 2. Image of a confirmed lunar Geminid impact, recorded on 14 December 2010 by Brian Cudnik. 2.3 Watching Spacecraft Crash The ALPO-LMIS, NASA-MSFC MEO and other organizations were active in monitoring any ground-based flashes or plumes produced by the impact of several spacecraft. The first was SMART-1 (European Space Agency) which was commanded to crash-land on the Moon on 2006 September 3. A campaign of ground-based amateur and professional telescopes and observatories was carried out, and nearly everyone observed a negative (i.e., no flash) 30

3 result. However, professional astronomers at the Canada-France-Hawaii Telescope Corporation recorded a flash in the infrared (2,122 nm) with the WIRCam wide-field infrared camera on the 3.6-meter optical/infrared telescope on the summit of Mauna Kea in Hawaii. The gif-animation posted on their website, shows nicely the flash followed by the resultant dust cloud of material kicked up by the impact. Nearly three years later, the Japanese Kaguya spacecraft was commanded to crash into the moon on 2009 June 10 at 18:25UT. This was daylight for North America so ALPO-LMIS did not coordinate this one. Astronomers in Asia were able to observe the impact flash resulting from this man-made event. Five months later, in 2009 October, the twin impacts of LCROSS (Lunar CRater Observation and Sensing Satellite) centaur upper stage rocket and LCROSS itself were observed from ground-based observatories all over the moon-facing hemisphere of the Earth. Nothing was observed from the ground, but LCROSS did capture plume images on its way to its own demise (Figure 3). It also detected signs of water (not the water itself, but two convincing signs that water is present, from the profile of the near infrared spectrum recorded by LCROSS s spectrometer to the ultraviolet signature of the hydroxyl (OH) molecule formed when H 2 O encounters solar radiation and is disassociated into H and OH molecules. 3. Current Work on Lunar Meteors 3.1 Lunar Meteoroid Impacts and how to Observe Them Published in 2010, this first-of-its-kind volume describes the various considerations that go into a lunar meteor monitoring program. It is a collection of work from various sources on all the stages involved in this sort of endeavor. This book provides a useful reference and training reference for those getting started with lunar meteor monitoring. It also provides resources for those who have been involved in astronomy for some time. As the name of the book implies, it starts with some background information about the cratering history of the moon and the history of LTP sightings from the 1500 s onward. The LTP catalog it provides focuses on events that resemble manifestations of meteoroid impacts and includes only the events that have the highest confidence ranking. Many of these were observed by skilled observers, giving the events significant credibility. The second half of the book focuses on the tools and techniques of lunar meteor observation. I focus on the video-equipped observer, but I also do not leave out the visual observer. I provide references and resources to provide observers with what is needed to carry out a fruitful campaign, and I share the dates of some of the more significant lunar meteor opportunities for years to come. 3.2 Current and Ongoing Efforts Figure 3. LCROSS image of impact plume generated by the crash of a centaur upper stage rocket seconds earlier. This event was instrumental in providing conclusive evidence for water ice existing in the permanently shadowed craters of the Moon s polar regions. Image courtesy of NASA. The ALPO-LMIS continues to coordinate a world-wide effort in monitoring the moon for meteoroid impacts. It does so through its website, through informal communication, papers at local conferences, and a list-server called lunarimpacts@yahoogroups.com. The level of activity and participation varies from year to year depending on the circumstances of the moon s position during annual meteor showers. NASA-MSFC also continues to monitor the moon regularly and has, as of 2011 November, recorded 233 impact candidates. Most of these are from sporadic meteors, but a number of annual showers are represented in the impact list. They monitor the moon about 10 nights per month, when the illumination is between 10 and 55 percent. The distribution of impacts may be more a reflection of where the monitoring is centered (from roughly ±30 degrees latitude and from 20% radius from disk center along the lunar equator to the limb). 31

4 Systematic imaging to study the ray structures of the moon at various phases not limited to full moon Imaging for photometric and radiometric studies Imaging of earthshine to gather information of the Earth s albedo over time Filtered and unfiltered imaging of the moon throughout its phase cycle to look for and characterize other forms of LTP High cadence observations of lunar eclipses to determine crossing times of lunar features by the Earth s shadow as well as estimates of contact times of the shadow with the lunar disk Figure 4. Map showing the locations of the 233 meteoroid impacts observed by NASA-MSFC from late 2005 to late The clustering of impact sites visible in the image may be more of a selection effect, refer to the text for more details. This image is courtesy of NASA-MSFC Meteoroid Environment Office. In both the ALPO and the NASA cases, monitoring takes place during a one week period from a few days after new until a day or two after first quarter, then again a day or two before last quarter until a few days before new. In these cases, the few days will last between 3 and 5 days, depending on ecliptic angle at a given observing location. If an annual shower is active, it will be monitored as part of the two week monitoring period, with a possible extension beyond the set periods to accommodate a shower peak or extend the monitoring due to lingering shower activity. Collaboration continues between NASA-MSFC and ALPO-LMIS. In both cases, the preferred monitoring method involves video and in both cases the video is analyzed by programs such as LunarScan or UFOCapture to capture the transient flashes. Usually one party discovers the event while the other party confirms with their videotapes and vice versa. 3.3 CMOS Imaging As part of our program to include new technologies (or at least technologies not widely used but potentially beneficial for research), we are also employing still imagery of the moon. We are using a CMOS (Complementary Metal Oxide Semiconductor) imager, assembled by Holland et al. (2008, 2009) to do systematic imaging of the illuminated lunar disk to look for several things (Cudnik et al., 2011a): Figure 5. Ground-based image of the entire lunar disk taken on 23 November 2010, obtained with a CMOS electronic detector and a Celestron NexStar 8-inch (20 cm) Cassegrain telescope. Image Credit: Prem Saganti, Gary Erickson, and Brian Cudnik. We will be working on the above in conjunction with other groups such as ALPO to maximize the value of our collaborative efforts. The goal is to enable the determination of a viable cause for other form of LTP in a similar manner as lunar meteor observations have been successfully used to validate and explain the point flash form of LTP. 3.4 Observing Program Nuts and Bolts We are always welcoming observations of the moon in search of lunar meteoroid impacts. Although we prefer the video method for observing and recording lunar meteors, we do not want to leave the visual observer out. Visual observers may be such due to personal preference or economics (financial difficulty preventing the purchase of equipment for video observation and data reduction). The advice I offer visual observers is this: ensure you are well rested and focused before your first observing ses- 32

5 sion, use a short wave radio and tape recorder and blank moon map to record your observed candidates, take frequent breaks after 10 or 15 minutes of observation to minimize fatigue (and resultant lost impact events), and finally, if there is any doubt, call it out anyway. Given the extremely transient nature of lunar meteoroid impacts, a very quick but noticed flash may very well turn out to be a genuine event. This, of course, is dependent on simultaneous video observation of the same region of the moon at the same time. This brings me to video observations. The active lunar meteor observer George Varros has an excellent tutorial on his website, which provides a handy walkthrough, from start to finish, of a typical observing run. A typical setup includes a telescope with a wide field of view, or a focal reducer, a low light black and white CCD video camera (like what people find with security vendors, an example is a Watec 902H2 Ultimate) a video time insertion / GPS device for recording time and geographic position, a recording device such as a digital video camcorder or a portable DVD recorder, and the means to store vast amounts of data. The equipment is set up to monitor the moon for one or more hours and the video is recorded for later analysis. One may also record nearby stars for magnitude estimates of any recorded impact candidate. Once the observing run is complete, or during the observing run if one is capable of doing so, the data is streamed into a program called LunarScan 1.5 written by Peter Gural, which takes 1 GB chunks of data and looks for impact candidates. The video stream is broken up into these chunks using a program called Virtual Dub. These chunks are then scanned frame by frame to look for meteoroid impact point flashes. Once a set of candidate impacts are found by the software, it is up to the user to weed out transients such as video noise or cosmic ray hits. After a list of likely candidates, including date, time, position, estimated magnitude, etc. is generated, this information is reported to NASA-MSFC and ALPO-LMIS. The observing team at NASA-MSFC may have been observing at the same time and can provide confirming observations of one or more of the impact candidates; the ALPO-LMIS serves to coordinate the former along with interested individuals and groups, they may be able to contact someone else observing at the same time to obtain a confirmation of one or more of the events observed. 3.5 Lessons Learned We have come a long way as far as lunar meteor monitoring is concerned. The technology has greatly improved since the early Leonid days of late 1999, and over twelve years of experience on many fronts have improved the techniques and approaches to lunar meteor observation. These are quite common events, but are randomized enough and of extremely short duration (20 to 100 milliseconds) so as to make them a significant challenge to observe. The presence of spurious events such as cosmic ray hits were quickly found to mimic real lunar meteor impact flashes, but closer inspection of these transients revealed subtle differences between these and true impact events. These differences include a fuzzy versus sharp flash profile, the flash appearing over multiple frames versus a single frame, etc. While these differences are not always easily discernible, knowing them did go a long way in helping to narrow down which events were more likely to be genuine events and which were not. The best, most foolproof means of determining whether an event is a genuine impact event remains this: to use two independent setups spaced at least 30 km apart observing at the same time to document the same event, within less than a second difference in event time and less than 5 difference in position on the moon s disk. 4. Upcoming Project: Observations in Support of the LADEE Mission The Lunar Atmosphere and Dust Environment Explorer (LADEE, Fig. 6) is a NASA spacecraft that will orbit the Moon and explore the dust and atmosphere environment at the moon. The mission is currently set for launch on a Minotaur-V launch vehicle in early 2013 July. After a 32 day cruise phase and a 30 day checkout period, the satellite will be ready to take data by mid-september. Unfortunately this is too late for a favorable Perseid encounter with the moon, which was originally going to be the focus of the collaborative effort. However, sporadic meteor impacts, regularly observed, will become the focus of observational efforts during the 60 day mission. The purpose of supplementing the LADEE mission with ground-based observations is to identify distinct impact events that are expected to kick up dust and inject it into the near-moon environment, replicating in some ways the days of Apollo 17 when sketches made by Eugene Cernan from lunar orbit showed some unusual optical phenomena minutes to seconds before orbital sunrise. Most noticeable of this is a set of crepuscular rays that seem to be caused by scattering attributed to particles or molecules of some type. In the airless environment of the moon, one would not expect to see any such phenomena. This leads to the question of what is replenishing the dust or material and how does it remain suspended above the lunar surface. 33

6 time at the University, and candidates will be logged, evaluated, reported, and catalogued. In addition to the university s efforts, I will be contacting existing and new collaborators to encourage them to put forward the effort to monitor the moon as often as they are able to each month, in support of existing regular campaigns. Ideally I would like to have a global network, monitoring the moon continuously (24 hours a day) for five days waxing and five days waning. But weather and a host of other influences will likely curtail this, but we will observe as much as we can. The monthly 10-day campaign will begin sometime later in 2012 and will continue prior to the launch of LADEE, and will continue through the science phase and afterwards. Impacts will be catalogued with me as coordinator of ALPO-LMIS and with NASA-MSFC, the Meteoroid Environment Office as part of their ongoing program. Sporadic meteoroid impacts happen fairly regularly and are expected to provide stimuli for, as well as an agent to maintain, the existing dusty environment in the vicinity of the moon. Meteoroid impacts are also thought to play a role in the replenishment of the lunar sodium exosphere (Bellot Rubio, et al., 2000). Figure 6. The LADEE spacecraft at the Moon, artist s conception. Image courtesy of NASA. To answer these questions, Dr. Brian Day of NASA-Ames has requested ground-based observations in collaborative support of the mission. These will be observations of lunar meteoroid impacts, made by interested amateur astronomers and participants at universities. The idea would be to characterize the source of the dust aloft by correlating increased fluxes of dust with impact events. If enough of these correlative events are documented, this effort will go a long way in answering the questions about what the Apollo astronauts (and unmanned Surveyor spacecraft) saw from the moon: the crepuscular rays and the horizon brightening just prior to sunrise. In preparation for this campaign, I will be upgrading the astronomical aspect of the department of Chemistry and Astronomy at Prairie View A&M University. The plan is to employ our physics majors to make the routine observations of the moon to match what NASA-MSFC is doing: for 10 days per month, monitor the moon (between 10% and 55% illumination) with a video camera and telescope system in search for meteoritic impacts. I plan to upgrade existing equipment to handle the expected heavy data load, and I plan to enable a semiautomated system to be run for each observing session. Data will be collected and analyzed in near real 5. Conclusion Professional-Amateur (pro-am) collaboration is enjoying a sort of golden age as professionals willingly seek out the assistance of amateurs in their research endeavors. The professionals have the training and the ideas, as well as the funding through grants and contracts, while the amateurs have the time and the equipment that could benefit a professional s project. Lunar meteor astronomy is an excellent example of pro-am collaboration at its finest. The Lunar Meteoritic Impact Search section of the Association of Lunar and Planetary Observers (referred to as ALPO-LMIS in this paper) has been coordinating the activities of interested amateur and professional astronomers since 2000 and has resulted in over 80 impact candidates being documented. A professional group at NASA, at the Marshall Space Flight Center (referred to as NASA-MSFC in the paper) Meteoroid Environment Office, coordinated by Dr. Bill Cook, has been regularly monitoring the moon for meteoroid impacts since late 2005 and as of 2011 November, have logged 233 impact candidates, most of which have been confirmed. Both groups have been working together for the last six years on lunar meteor observation and collaboration. A NASA mission to the moon, to be launched in 2013 July, is the Lunar Atmosphere and Dust Environment Explorer (LADEE), which is expected to 34

7 better our understanding of the lunar dust environment and connections between suspended dust and meteoroid impacts. ALPO-LMIS has been asked to collaborate with them during the mission timeframe (late summer to early fall 2013) to observe meteoroid impacts on the moon in order to help correlate increases in dust abundance with meteoroid impacts. This partnership will be an excellent one to further our understanding of the near-moon environment, including the moon s exosphere and changes to it related to impacts. Anyone who is interested in contributing to the LADEE portion of the campaign, or the general lunar monitoring campaign is encouraged to contact me or visit for more information. 6. Acknowledgements I want to thank Robert Buchheim for encouraging me to share with the Society of Astronomical Sciences the work I am helping to coordinate. I am thankful for Dr. Premkumar Saganti, my colleague at Prairie View A&M University for his support and encouragement. I also thank Brian Day for providing the opportunity for collaboration between a worthwhile space-based mission and a worthy groundbased observing program. Finally, many thanks go to Mr. Doug Holland for providing the CMOS detector and all the help in its operation. 7. References Beech, M. and Nikolova, S. (1998). Leonid flashersmeteoroid impacts on the Moon. Il Nuovo Cimento, Note Brevi 21C, Holland D.. et al. (2008). U.S. Patent Holland D., et al. (2009). U.S. Patent Cudnik, B. M., Saganti, P. B., Erickson, G. M. (2011). Imaging Detectors in Planetary and Space Science. 42nd Lunar and Planetary Science Conference, 2011 March 7 11 at The Woodlands, Texas. No. 1608, p Bellot Rubio, L. R., Ortiz, J. L., Sada, P.V. (2000). Observation and Interpretation of Meteoroid Impact Flashes on the Moon. Earth Moon and Planets, 82/83,